This invention relates to the field of concrete construction and more particularly to the field of concrete construction formwork and apparatus for assembling such formwork into functional units. Specifically, this invention relates to apparatus for tying formwork panels together by means of elongated ties and fastening devices attachable to the panels to secure the ties and panels against relative movement.
To construct concrete forms from panels maintained in spaced opposed relationship, numerous prior art devices have been proposed and utilized with varying degrees of success. These devices have generally comprised a rod extending between and through both such panels with varying forms of wedging or locking devices provided to grip the ends of the tie and thus prevent outward movement of the form panels. With devices of this nature the forms are generally provided with spacers to prevent inward movement thereof, and the rod end fastening devices are attached to walers on the form panels. The rod end fastening devices have generally taken the form of loops through which hooks are inserted, nuts threaded onto the end of a threaded tie, or a hot-upset "button" end similar to the head of a nail or bolt. A major disadvantage that all such apparatus has suffered has been the difficulty of removal of the fastening device after the concrete structure has been poured and set. This problem is caused by the expansion of the concrete during setting greatly increasing the outward pressure against the form panels and thus against the tie rod end fastening devices. Accordingly, it has required great force to release these prior art devices in order to remove the form panels. This difficulty in removing the fastening devices has resided principally in the inability of such devices to release the longitudinal stresses on the rods quickly upon the initiation of the releasing action. Another disadvantage suffered by the structures using threaded ties and nuts or ties with enlarged headed ends has been their inability to compensate for misalignment between the tie and the clamping structure on the form panel. Misalignment of these prior art devices, generally manifested by angular displacement of the tie from a line normal to the form panel, has generally resulted in the imposition of the entire longitudinal stress upon one corner or a very small portion of this tie end anchoring structure. This condition not only increases the difficulty of releasing the clamp but also imposes severe bending stresses on the tie, possibly leading to its failure.
In view of the foregoing disadvantages of the prior art devices it is an object of this invention to provide concrete form panel tying apparatus which may quickly and easily be installed to clamp form panels into place and may quickly and easily be removed to release such panels, even when such panels are under great pressure from the concrete structure formed within. It is another object of this invention to provide concrete form panel tying apparatus which compensates for some amount of misalignment between the tie and the form panel and avoids the imposition of excessive point loadings and bending stresses upon the tie.